Polysilanes are attracting attention for their use as ceramic precursors; optoelectric materials such as photoresist, organic photosensitive material, optical waveguide, and optical memory, etc.
Heretofore, a method for producing polysilane is known wherein dialkyldihalosilane or dihalotetraalkyldisilane dissolved in toluene is subjected to reductive coupling in the presence of alkali metals such as metallic sodium with thorough stirring at a temperature over 100.degree. C. (J. Am. Chem. Soc., 103 (1981) 7352). This method, however, including the steps of heating, thoroughly stirring and dispersing alkali metal which is inflammable in the presence of air, has safety problems for industrial-scale production. Further, the quality of the polysilane produced by this method is unsatisfactory; its molecular-weight distribution is polymodal, for example.
To overcome these drawbacks, several new methods for producing polysilanes have been proposed, as described below.
(a) Anionic polymerization of disilenes masked by biphenyl or the like. (Japanese Unexamined Patent Publication No. 23063/1989).
(b) Ring-opening polymerization of cyclic silanes (Japanese Unexamined Patent Publication 170913/1993).
(c) Dehydrogenative polycondensation of hydrosilane in the presence of transition-metal complex catalyst (Japanese Unexamined Patent Publication No. 17753/1995).
(d) Electroreduction of dihalosilane at room temperature or lower temperatures (Japanese Unexamined Patent Publication 309953/1995).
However, the above methods (a) and (b) suffer from various defects: they require complicated processes for producing monomers, the total yield of monomer is low in synthesis, and there are safety concerns due to the alkyl lithium reagent employed in polymerization. The method (c) has yet to be improved in the molecular weight and the structure of resulting polysilane (e.g., formation of crosslinked structure) attributable to the reaction mechanism thereof.
The method (d), on the other hand, is an excellent technique for providing high-molecular-weight and high-quality polysilane safely and efficiently in a high yield. The method, however, requires a special reaction apparatus, i.e., electrolytic cell. Accordingly, the method is not suitable for producing polysilane for less valuable applications although very useful for producing polysilanes for highly valuable applications.
In view of the above, it is a principal object of the present invention to provide a new method for producing desired polysilanes without complicated operations, and safely and economically.